An aerial work engineering machine, such as an elevating fire engine, is a product having a specialized chassis and mounted with a lifting arm frame, and may be operated by a professional operator to rise to a certain height for aerial rescuing or working.
The lifting arm frame may be divided into several types according to the lifting operation manner, such as a folding arm type, a telescopic arm type, a combined arm type and a self-propelled type. The telescopic arm is formed by two or more sections of box-shaped arms sleeved together, and may be driven by a telescopic cylinder or pulled by a flexible wire rope or a leaf chain to make linear reciprocating motion, and may transport an aerial operator to a higher place for working via a bucket mounted on a head of the telescopic arm.
For example, a fire water cannon is arranged at a top end of the telescopic arm of the elevating fire truck, and mechanisms, such as a working platform, is arranged at the top end of the telescopic arm of the aerial work platform. The operator can control the telescopic arm on the controlling platform to realize aerial work functions, such as spraying water, transporting working personnel, or rescuing.
With the rapid development of the social economy of China, the number of high-rise and super-high-rise buildings is growing rapidly, resulting in unprecedented tremendous challenges in fire extinction and emergency rescue of the high-rise buildings. In China, the development of the elevating fire truck has a tendency of pursuing a higher and higher working altitude, and at the same time, the high-altitude and super-high-altitude elevating fire trucks has higher requirements on the performances of the telescopic system, such as safety, reliability and smoothness.
The telescopic arm of the high-working-altitude elevating fire truck has a long stroke and has large numbers of sections, thus a single-cylinder and multi-stage telescopic-chain-type synchronous telescopic control system has been unable to meet the requirements for safety and stability. And for a telescopic system having two or more telescopic cylinders, the telescopic cylinders have to be controlled synchronously so as to reach the maximum working height in the shortest action time to perform the rescue operation quickly.
None of the existing elevating fire trucks using a dual-cylinder telescopic system are provided with a synchronous control valve, and the motion of the telescopic cylinders is controlled directly by a solenoid directional valve group.
Reference is made to FIG. 1, which is a hydraulic schematic diagram of the solenoid directional valve group of the existing dual-cylinder telescopic system.
As shown in the Figure, an upper telescopic cylinder 1 is controlled by a first solenoid directional valve 3-1, and a lower telescopic cylinder 2 is controlled by a second solenoid directional valve 3-2. A solenoid directional valve group 3 is formed by the first solenoid directional valve 3-1 and the second solenoid directional valve 3-2, and has oil ports A1 and B1 connected to a larger chamber and a smaller chamber of the upper telescopic cylinder 1 respectively, and oil ports A2 and B2 connected to a larger chamber and a smaller chamber of the lower telescopic cylinder 2 respectively. Theoretically, the upper telescopic cylinder 1 and the lower telescopic cylinder 2 can be controlled to extend or retract synchronously as long as the first solenoid directional valve 3-1 and the second solenoid directional valve 3-2 are synchronously switched to the left position or the right position.
However in fact, since the load on the lower telescopic cylinder 2 is much larger than the load on the upper telescopic cylinder 1, the extending and retracting motion of the two cylinders may have two circumstances. Taking the extending motion as an example, if the system flow is large enough, the two cylinders may extend synchronously, but the upper telescopic cylinder 1 will have an extending speed faster than the lower telescopic cylinder 2 and will reach the end of the stroke earlier. In contrast, if the system flow is small, the pressure oil will firstly push the upper telescopic cylinder 1 with a smaller load to extend via the directional valve, and after the upper telescopic cylinder 1 reaches the end, the system pressure increases, and then the pressure oil will continue to push the lower telescopic cylinder 2 to extend till the lower telescopic cylinder 2 reaches the end.
This kind of control systems have disadvantages that, the synchronous extension and retraction of the two cylinders can not be realized, and the two telescopic cylinders are controlled separately to extend to the end of the stroke in sequence, which may cause an overlong action time of the telescopic system, and further affect efficiencies of rescue operation and work.
Therefore, a technical problem to be solved by those skilled in the art is to control two cylinders of the dual-cylinder telescopic system to extend and retract synchronously so as to shorten the action time of the telescopic system and improve the working efficiency.